1. Field of the Invention
The present invention relates to a power transmission system of a hybrid electric vehicle, and more particularly, to a power transmission system of a hybrid electric vehicle that can suppress conversion to an ENG mode by providing sufficient power performance at the time of wide open throttle (WOT) launching and maximally use power of an engine at the time of conversion to a first HEV mode and a third HEV mode.
2. Description of Related Art
Eco-friendly technology of a vehicle is a core technology influencing survival of a future vehicle industry and advanced vehicle makers devote all their might to developing eco-friendly vehicles for meeting environmental and fuel efficiency regulations.
As a result, the respective vehicle makers have developed an electric vehicle (EV), a hybrid electric vehicle (HEV), a fuel cell electric vehicle (FCEV), and the like as a future vehicle technology.
Since the future vehicle has various technological restrictions such as a weight and cost, the vehicle makers have paid attention to the hybrid electric vehicle as an alternative of a realistic problem for meeting exhaust gas regulations and improving fuel efficiency performance and have entered into keen competition for commercializing the hybrid electric vehicle.
The hybrid electric vehicle is a vehicle using two or more power sources. Two or more power sources may be combined by various schemes and a gasoline engine or a diesel engine using the existing fossil fuel and a motor/generator driven by electric energy are mixed and used as the power sources.
In the hybrid electric vehicle, an EV mode in which the hybrid electric vehicle is driven by only the motor, an HEV mode using both the engine and the motor, and an ENG mode using only the engine can be implemented according to the combination of the engine and the motor.
Further, the hybrid electric vehicle can acquire a significant fuel efficiency enhancement effect as compared with the existing vehicle through idle stop of stopping the engine when the vehicle stops, fuel saving by regenerative braking that drives a generator by using kinetic energy of the vehicle instead of braking by the existing friction when the vehicle is braked, and stores in a battery electric energy generated at the time of driving the generator and reuses the stored electric energy in driving the vehicle, and the like.
A power transmission system of the hybrid electric vehicle is classified into a single-mode scheme and a multiple-mode scheme.
The single-mode scheme has an advantage that torque transmission mechanisms such as a clutch and a brake for transmission control are not required, but disadvantages that when the vehicle travels at a high speed, efficiency deteriorates, and as a result, the fuel efficiency is low and an additional torque increasing device is required to apply the single-mode scheme to large-sized vehicles.
The multiple mode scheme has advantages that when the vehicle is driven at the high speed, the efficiency is high and torque can be designed to increase, and as a result, the multiple-mode scheme can be applied to large and medium-sized vehicles.
As a result, in recent years, the multiple-mode scheme has primarily been adopted rather than the single-mode scheme and the resulting research has actively progressed.
The multiple-mode scheme power transmission system is configured to include a plurality of planetary gear sets, a plurality of motors/generators used as the motor and the generator, a plurality of torque transmission mechanisms (friction elements) capable of controlling rotating elements of the planetary gear sets, a battery used as power sources of the motors/generators, and the like.
The multiple-mode scheme power transmission system has different operating mechanisms according to connection configurations of the planetary gear sets, the motors/generators, and the torque transmission mechanisms.
In addition, since the multiple-mode scheme power transmission system has characteristics that durability, power transmission efficiency, a size, and the like vary according to the connection configurations, research and development for implementing a power transmission system which is stronger, has no power loss and is compact has been continued, in a power transmission system field of a hybrid electric vehicle.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.